1. Field of the Invention
This invention generally relates to wireless communications telephone devices and, more particularly, to a system and a method for acquiring a channel when activating a wireless telephone device.
2. Description of the Related Art
When a wireless communications telephone device is first activated, the wireless device must obtain initialization information and a list of channels to which the wireless device can connect. The initialization information enables the wireless device to find a suitable radio carrier channel and obtain carrier system information. The initialization information is typically included in a Number Assignment Module (NAM) pre-loaded into the wireless device memory. The appropriate NAM also can be loaded by the wireless device user into the wireless device using a wireless device user interface. If more than one NAM is pre-loaded in wireless device memory, it is known to have the wireless device user manually select a NAM appropriate for the current wireless device location. However, the wireless device does not include a means for automatically selecting the appropriate NAM. NAMs generally cover relatively large geographical areas, such as a metropolitan region. Within these geographical areas there can be a large number of cells or coverage areas. A Priority Roaming List (PRL) in the NAM typically includes a listing of channel groups. Each channel group is associated with a channel coverage area within the area covered by the NAM and includes the channels for the respective channel coverage area. Typically, a wireless telephone user has a contract for services from a particular carrier or provider. Each network carrier has preferences regarding the channels a wireless device acquires in a given channel coverage area. Therefore, the channels in a given channel group are listed according to the carrier's preference. The PRL also includes system information such as base station Network Identification (NID).
Once initialization information, such as the wireless device telephone number, is loaded, the wireless device begins the process of acquiring a channel by scanning the channels listed in the PRL. In general, the wireless device begins with the first channel group in the PRL and scans additional groups in the order in which the groups are listed in the PRL. The wireless device scans the channels to acquire a pilot signal with sufficient signal strength. After acquiring a pilot signal, the wireless device acquires the associated synch signal containing system information for the pilot signal channel, such as the NID and the System Identification (SID). The wireless device then compares the synch signal system information with system information listed for the channel in the PRL. If the system information matches, the pilot signal is from a base station within the coverage area for the current wireless device location and the wireless device acquires the pilot signal channel. Otherwise, the pilot signal is from a base station outside the coverage area and the wireless device begins scanning again, starting with the next channel listed in the PRL.
In some cases, the wireless device contains a Most Recently Used Table (MRU) listing the channels to which the wireless device has most recently been connected. Upon activation, the wireless device can begin scanning channels listed in the MRU. If the wireless device has not moved too far from the location in which it was last deactivated, a suitable channel may be found in the MRU. Otherwise, the MRU is no longer useful (that is, the channels in the MRU are for coverage areas other than the coverage area in which the wireless device is currently located) and the wireless device must scan channels in the PRL as noted above.
Once a wireless device acquires a channel as described above, there are known handoff procedures that enable the wireless device to acquire different channels as the wireless device moves among various cells within a selected NAM coverage area. However, if the wireless device moves into an adjoining NAM coverage area, the known handoff procedures cannot be used since the selected NAM does not contain initialization information or a PRL for the adjoining NAM. In this case, the wireless device goes into deep sleep. That is, the wireless device continues to scan for a pilot signal associated with the selected NAM, but increases the time period between scans to minimize battery usage. It is known to manually load a new NAM when leaving the coverage area for a selected NAM. However, as noted above, the wireless device cannot automatically select an appropriate NAM.
A PRL can contain a large number of channels. Therefore, acquiring a channel by scanning channels, beginning at the top of the PRL, can take a significant amount of time, particularly if the desired channel group is near the end of the channel group listings in the PRL. Unfortunately, the wireless device is unable to carry out communications functions, such as receiving pages, while scanning channels from the PRL. Therefore, during PRL channel scans, wireless device users are deprived of the use of their devices and carriers are deprived of revenue-generating activity. These same disadvantages also apply to the case in which a wireless device moves out of the coverage area for a selected NAM and loses its operating channel. In addition, lengthy scan times place an extra burden on wireless device batteries.
It would be advantageous if the time needed to acquire a channel when activating a wireless device could be reduced.